Variation within this widespread eastern annual and its relatives needs further study. Although usually found in damp acid grasslands, it can occur in quite varied habitats, including calcareous soils outside Ky. (Pennell 1935; W). A. purpurea is close to the more southeastern species, fasciculata, with some apparent intergradation; see notes under that name. A coll. from ROWA is referable to the more northern taxon, A. purpurea var. parviflora (Benth.) Boivin, which some recent authors (W) have recognized as a species: A. paupercula (Gray) Britt. However, its label data are dubious (Campbell et al. 1992). This taxon differs in its more deeply dissected calyx, with lobes 2-3.5 mm long (versus 0.5-2 mm). Also, flowers tend to be smaller in general (F). The disjunct population of plants referred to paupercula in s. Ill. (K) deserves further investigation; similar plants may occur in open post oak woods of MARS, CALL and w. Tenn. (M. Brock, pers. comm.).